Lash adjuster

ABSTRACT

The object is to prevent rotation of the case when a load is applied to the adjusting screw that tends to push in the adjusting screw. 
     The lash adjuster includes a cylindrical case  13  having a bottom  17  and received in a mounting hole  6  formed in a top surface of a cylinder head  2,  the case  13  having an internal thread  14  on an inner periphery thereof, an adjusting screw  16  having an external thread  15  on an outer periphery thereof which is in threaded engagement with the internal thread  14  of the case  13,  and a return spring  18  disposed between the adjusting screw  16  and the bottom  17  of the case  13  and biasing the adjusting screw  16  in a direction to protrude upwardly from the case  13,  the adjusting screw  16  having a protruding end  22  protruding from the case  13  and configured to pivotally support an arm  7  of a valve gear, wherein an anti-rotation protrusion  27  is provided on the bottom  17  of the case  13  which is fitted in a fitting port  26  formed in an inner bottom surface  24  of the mounting hole  6,  thereby preventing rotation of the case  13.

TECHNICAL FIELD

This invention relates to a lash adjuster mounted in a valve gear for an engine.

BACKGROUND ART

One known valve gear for moving a valve provided at an intake port or an exhaust port of an engine includes an arm pivotable about one end thereof and adapted to be pressed down at its mid-portion by a cam, thereby pressing down the valve stem at its other end.

With this valve gear, while the engine is running, due to differences in thermal expansion between component parts of the valve gear, gaps between component parts of the valve gear may change, thereby producing noise or causing pressure leakage. When sliding parts of the valve gear become worn too, gaps between component parts of the valve gear change, thus producing noise or causing pressure leakage.

In order to prevent such noise and pressure leakage, a typical valve gear includes a lash adjuster to eliminate gaps between component parts of the valve gear.

Typically, such a lash adjuster comprises a cylindrical case having a bottom and received in a mounting hole formed in the top surface of the cylinder head, an adjusting screw having an external thread on the outer periphery thereof which is in threaded engagement with an internal thread formed on the inner periphery of the case, and a return spring biasing the adjusting screw in the direction to protrude upwardly from the case, thereby pivotally supporting the arm of the valve gear at the protruding end of the adjusting screw protruding from the case (Patent documents 1 and 2).

In the arrangement of Patent document 1, the return spring is a compression coil spring that applies an axial force to the adjusting screw that tends to push the adjusting screw out of the case. In the arrangement of Patent document 2, the return spring is a torsion spring that applies torque to the adjusting screw that tends to push the adjusting screw out of the case.

With these lash adjusters, when the cam rotates and a load is applied to the adjusting screw that tends to push in the adjusting screw, the external thread of the adjusting screw is supported by the internal thread of the case, so that the adjusting screw is axially fixed in position.

If the relative position between the arm and the cylinder head changes due e.g. to thermal expansion of the valve gear, according to the change in relative position, the adjusting screw axially moves in the case while rotating relative to the case, thereby absorbing the change in gaps between component parts of the valve gear.

Patent document 1: JP Patent Publication 2005-273510A Patent document 2: JP Patent Publication 64-34407A

DISCLOSURE OF THE INVENTION Object of the Invention

With these adjusters, since the outer periphery of the case and the inner periphery of the mounting hole are both cylindrical surfaces, when a force in the rotational direction is applied to the case, the case rotates relative to the mounting hole. Particularly while the engine is running and the temperature of the valve gear is high, the case tends to easily rotate relative to the case, because in this state, a gap forms between fitting surfaces of the case and the mounting hole due to a difference in thermal expansion between the cylinder head and the case.

Thus, with these lash adjusters, when the cam rotates and a load is applied to the adjusting screw that tends to push in the adjusting screw, the case may rotate relative to the mounting hole under the force that acts between the thread surfaces of the adjusting screw and the case. If the case rotates, the adjusting screw is pushed into the case, reducing the valve lift. Rotation of the case would also quicken wear of the mounting hole.

An object of the present invention is to prevent rotation of the case when a load is applied to the adjusting screw that tends to push in the adjusting screw.

Means to Achieve the Object

In order to achieve this object, the lash adjuster is provided with an anti-rotation means for preventing rotation of the case.

The anti-rotation means may comprise an anti-rotation protrusion provided on the bottom of the case, and a fitting port formed in an inner bottom surface of the mounting hole, in which the anti-rotation protrusion is fitted. With this arrangement, the case is prevented from rotating due to engagement of the anti-rotation protrusion in the fitting port.

The anti-rotation protrusion may be a protrusion having a D-cut portion on an outer periphery thereof, a protrusion having two chamfers on an outer periphery thereof, a protrusion in the shape of a regular polygonal column, or a protrusion offset from an axis of the case.

The fitting port may be one end of an air vent hole extending from the inner bottom surface of the mounting hole to outside. With this arrangement, when the lash adjuster is inserted into the mounting hole, air between the bottom of the case and the inner bottom surface of the mounting hole is discharged through the air vent hole, so that the interior of the mounting hole is kept at the atmospheric pressure, which prevents reaction force from acting on the bottom of the case. Thus, the lash adjuster can be mounted easily in the cylinder head. Since one end of the air vent passage is used as the fitting port, there is no need to form the fitting port separately from the air vent hole, which makes easier to form the cylinder head.

A through hole may be formed to extend vertically through the bottom of the case, with a bottom end thereof open to a free end of the anti-rotation protrusion. With this arrangement, since engine oil flowing into the case through between the external thread of the adjusting screw and the internal thread of the case is discharged through the through hole and then the air vent hole, soot and other contaminants mixed into engine oil is less likely to get stuck between the external thread of the adjusting screw and the internal thread of the case, which makes the external thread and the internal thread less likely to become worn.

The anti-rotation means may be a friction ensuring means for ensuring frictional resistance between the bottom of the case and the inner surface of the mounting hole, thereby preventing rotation of the case.

The friction ensuring means comprises an oil film expelling groove formed in an outer bottom surface of the case. With this arrangement, engine oil present between the outer bottom surface of the case and the inner bottom surface of the mounting hole is released into the oil film expelling grooves. This prevents formation of oil film between the outer bottom surface of the case and the inner bottom surface of the mounting hole due to the squeezing effect, which in turn ensures sufficient frictional resistance between the outer bottom surface of the case and the inner bottom surface of the mounting hole.

The friction ensuring means may comprise a satin-finished surface formed on the outer bottom surface of the case. With this arrangement, compared to an arrangement in which the outer bottom surface of the case is flat and smooth, the outer bottom surface of the case has a higher friction coefficient, so that it is possible to ensure sufficient frictional resistance between the outer bottom surface of the case and the inner bottom surface of the mounting hole. The outer bottom surface of the case may be satin-finished by electric discharge machining or laser machining. But preferably, it is satin-finished by shot peening, because shot peening hardens the outer bottom surface of the case, thereby increasing its wear resistance.

The friction ensuring means may comprise a tapered outer peripheral surface formed on the bottom of the case and having a downwardly decreasing diameter, and a tapered inner peripheral surface formed on the mounting hole and having a downwardly decreasing diameter, with the tapered outer peripheral surface engaged in the tapered inner peripheral surface. With this arrangement, high surface pressure is produced between the tapered outer peripheral surface and the tapered inner peripheral surface due to the wedge effect, which ensures sufficient frictional resistance between the tapered outer peripheral surface and the tapered inner peripheral surface.

The friction ensuring means may comprise a recess formed in the outer bottom surface of the case except its peripheral edge. With this arrangement, frictional resistance produced between the outer bottom surface of the case and the inner bottom surface of the mounting hole concentrates on the radially outer side, so that it is possible to ensure sufficient frictional resistance for preventing rotation of the case. Alternatively, a similar recess may be formed in the inner bottom surface of the mounting hole except its peripheral edge as the friction ensuring means.

The friction ensuring means may comprise a small-diameter inner peripheral portion formed on the mounting hole, the bottom of the case being press-fitted in the small-diameter inner peripheral portion. With this arrangement, high surface pressure is produced between the bottom of the case and the small-diameter inner peripheral portion due to press fitting, which ensures sufficient frictional resistance between the bottom of the case and the inner surface of the mounting hole.

The friction ensuring means may comprise a sheet made of rubber or an elastomer and disposed between an outer bottom surface of the case and the inner bottom surface of the mounting hole. With this arrangement, the frictional resistance between the outer bottom surface of the case and the inner bottom surface of the mounting hole is higher than when the outer bottom surface of the case is in direct contact with the inner bottom surface of the mounting hole, so that it is possible to ensure sufficient frictional resistance for preventing rotation of the case.

The friction ensuring means may comprise a seat made of iron and forming the inner bottom surface of the mounting hole. With this arrangement, since the inner bottom surface of the mounting hole is less likely to become worn, even if the cylinder head is made of aluminum, it is possible to minimize reduction with time in friction coefficient of the inner bottom surface of the mounting hole, thus ensuring sufficient frictional resistance between the bottom of the case and the inner surface of the mounting hole.

The friction ensuring means may comprise a sleeve made of iron and forming the mounting hole. With this arrangement, since the inner surface of the mounting hole is less likely to become worn, even if the cylinder head is made of aluminum, it is possible to minimize reduction with time in friction coefficient of the inner surface of the mounting hole, thus ensuring sufficient frictional resistance between the bottom of the case and the inner surface of the mounting hole.

The return spring may be a compression coil spring that applies an axial force to the adjusting screw that tends to push the adjusting screw out of the case. Alternatively, the return spring may be a torsion spring that applies torque to the adjusting screw that tends to push the adjusting screw out of the case. The torsion spring may be one of a torsion coil spring, a spiral spring and a volute spring.

The external thread and the internal thread are triangular threads, trapezoidal threads or serration-shaped threads.

ADVANTAGES OF THE INVENTION

Since the lash adjuster according to this invention is provided with an anti-rotation means for preventing rotation of the case, the case is less likely to rotate when a load is applied to the adjusting screw that tends to push in the adjusting screw. This prevents reduction in the valve lift due to rotation of the case. The lash adjuster thus stably performs its function. Also, it is possible to prevent wear of the inner surface of the mounting hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a valve gear including a lash adjuster according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the lash adjuster of FIG. 1 and its surrounding area.

FIG. 3 is a sectional view taken along line III-III of FIG. 2.

FIG. 4 is an enlarged view of a different anti-rotation protrusion from that of FIG. 2.

FIG. 5 is a sectional view taken along line V-V of FIG. 4.

FIG. 6 is an enlarged view of a still different anti-rotation protrusion from that of FIG. 2.

FIG. 7 is a sectional view taken along line VII-VII of FIG. 6.

FIG. 8 is an enlarged sectional view of a further different anti-rotation protrusion from that of FIG. 2.

FIG. 9 is a sectional view taken along line IX-IX of FIG. 8.

FIG. 10 is an enlarged sectional view of a lash adjuster according to a second embodiment of the present invention.

FIG. 11 is an enlarged sectional view of a modification of the return spring shown in FIG. 10.

FIG. 12 is an enlarged sectional view of another modification of the return spring shown in FIG. 10.

FIG. 13 is a sectional view taken along line XIII-XIII of FIG. 12.

FIG. 14 is an enlarged sectional view of still another modification of the return spring shown in FIG. 10.

FIG. 15 is an enlarged sectional view of a lash adjuster according to a third embodiment of the present invention.

FIG. 16 is a sectional view taken along line XVI-XVI of FIG. 15.

FIG. 17 is an enlarged sectional view of a modification of the means of ensuring friction shown in FIG. 15.

FIG. 18 is an enlarged sectional view of another modification of the means of ensuring friction shown in FIG. 15.

FIG. 19 is an enlarged sectional view of still another modification of the means of ensuring friction shown in FIG. 15.

FIG. 20 is an enlarged sectional view of a further modification of the means of ensuring friction shown in FIG. 15.

FIG. 21 is an enlarged sectional view of a still further modification of the means of ensuring friction shown in FIG. 15.

FIG. 22 is an enlarged sectional view of still another modification of the means of ensuring friction shown in FIG. 15.

FIG. 23 is an enlarged sectional view of still another modification of the means of ensuring friction shown in FIG. 15.

DESCRIPTION OF THE DRAWINGS

-   1. Lash adjuster -   2. Cylinder head -   6. Mounting hole -   7. Arm -   13. Case -   14. Internal thread -   15. External thread -   16. Adjusting screw -   17. Bottom -   18. Return spring -   22. Protruding end -   24. Inner bottom surface -   25. Air vent hole -   26. Fitting port -   27. Anti-rotation protrusion -   28. D-cut portion -   30. Through hole -   31. Two chamfers -   32, 35, 37. Anti-rotation protrusion -   41, 51. Lash adjuster -   52. Outer bottom surface -   53. Oil film expelling groove -   54. Tapered inner peripheral surface -   55. Tapered outer peripheral surface -   56. Recess -   57. Small-diameter inner peripheral portion -   58. Sheet -   59. Seat -   61. Sleeve

BEST MODE FOR EMBODYING THE INVENTION

FIG. 1 shows a valve gear including a lash adjuster 1 according to a first embodiment of the present invention. This valve gear includes a valve 4 provided at an intake port 3 of a cylinder head 2 of an engine, a valve stem 5 connected to the valve 4, a lash adjuster 1 mounted in a mounting hole 6 formed in the top surface of the cylinder head 2, and an arm 7 supported by the lash adjuster 1 so as to be pivotable about the lash adjuster 1.

The valve stem 5 extends upwardly from the valve 4 and slidably through the cylinder head 2. An annular spring retainer 8 is fixed to the outer periphery of the valve stem 5 at its upper portion. A valve spring 9 is mounted between the bottom surface of the spring retainer 8 and the top surface of the cylinder head 2. The valve spring 9 biases the valve stem 5 upwardly through the spring retainer 8, thereby seating the valve 4 against a valve seat 10 by its biasing force.

The arm 7 has one end thereof supported by the lash adjuster 1 and the other end in contact with the top end of the valve stem 5. At its mid-portion, the arm 7 carries a roller 11 which is in contact with a cam 12 provided over the roller 11.

As shown in FIG. 2, the lash adjuster 1 comprises a cylindrical case 13 having a bottom and inserted in the mounting hole 6, an adjusting screw 16 having an external thread 15 on its outer periphery at its lower portion which is threaded engagement with an internal thread formed on the inner periphery of the case 13, and a return spring 18 mounted between the adjusting screw 16 and the bottom 17 of the case 13.

The external thread 15 and the internal thread 14 each have a pressure flank that receives pressure when a load is applied that tends to push the adjusting screw 16 into the case 13. The pressure flank 19 has a flank angle larger than the clearance flank 20 so that the threads 15 and 14 have a serration-shaped section.

The return spring 18 is a compression coil spring having its bottom end supported by the bottom 17 of the case 13 and applies, at its top end, an axial force to the adjusting screw 16 through a spring seat 21 that tends to push the adjusting screw 16 upwardly out of the case 13.

As shown in FIG. 1, the adjusting screw 16 has a protruding end 22 protruding from the case 13 and fitted in a recess 23 formed in the bottom surface of the arm 7 at its end, thus supporting the arm 7 so as to be pivotable about the protruding end 22. An air vent hole 25 is formed in the cylinder head 2 to extend from an inner bottom surface 24 of the mounting hole 6 to outside. When the lash adjuster 1 is inserted into the mounting hole 6, air between the case 13 and the inner bottom surface 24 of the mounting hole 6 is discharged through the air vent hole 25.

As shown in FIG. 2, an anti-rotation protrusion 27 is formed on the bottom 17 of the case 13 which is fitted in a fitting port 26 formed in the inner bottom surface 24 of the mounting hole 6. The fitting port 26 constitutes one end of the air vent hole 25. The anti-rotation protrusion 27 has a D-cut portion 28 on its outer periphery which engages a D-cut portion 29 formed on the inner periphery of the fitting port 26, thereby rotationally fixing the case 13 in position. The D-cut portion 28 is formed by cutting the outer periphery of the protrusion 27 along a plane parallel to a plane including the axis of the case 13.

The case 13 is made of iron to ensure strength of the internal thread 14. The fitting port 26, which has the D-cut portion 29 on its inner periphery, and the air vent hole 25, which has the fitting port 26 at one end, can be formed when forming the cylinder head 2 by die-casting aluminum.

As shown in FIG. 2, a through hole 30 extends vertically through the bottom 17 of the case 13 with its bottom open to the bottom end surface of the anti-rotation protrusion 27. Thus, engine oil flowing into the case 13 from its top end surface through the gap between the external thread 15 and the internal thread 14 is discharged from the case 13 through the through hole 30 and then the air vent hole 25.

Now the operation of the lash adjuster 1 is described.

While the engine is running, as the cam 12 rotates and the cam lobe 12 a of the cam 12 presses the arm 7, the valve 4 separates from the valve seat 10, opening the intake port 3. At this time, a load is applied to the adjusting screw 16 that tends to push in the adjusting screw. But since the pressure flank 19 of the external thread 15 is supported by the pressure flank 19 of the internal thread 14 in this state, the adjusting screw 16 is axially fixed in position. Also, torque is applied between the pressure flanks 19 of the external thread 15 and the internal thread 14. But the case 13 never rotates due to engagement between the anti-rotation protrusion 27 and the fitting port 26.

As the cam 12 further rotates and the cam lobe 12 a moves past the roller 11, the valve stem 5 rises under the biasing force of the valve spring 9, so that the valve 4 is seated on the valve seat 10, closing the intake port 3.

Strictly speaking, when the arm 7 is pressed down by the cam lobe 12 a of the cam 12, slight slip occurs between the pressure flanks 19 of the external thread 15 and the internal thread 14, thus pushing in the adjusting screw 16. But once the cam lobe 12 a moves past the roller 11 and the load that tends to push in the adjusting screw is removed, the adjusting screw 16 returns to the original position under the load from the return spring 18 which tends to push out the adjusting screw.

While the engine is running, if the distance between the cam 12 and the arm 7 increases due to thermal expansion differences between component parts of the valve gear such as the cylinder head 2, valve stem 5 and arm 7, the adjusting screw 16 protrudes by a larger amount when the cam 12 further rotate after the cam lobe 12 a of the cam 12 presses down the arm 7 until the load is removed, than the amount by which the adjusting screw 16 is pushed in when the arm 7 is pressed down by the cam lobe 12 a of the cam 12. As a result, every time the cam 12 rotates once, the adjusting screw 16 protrudes gradually, thus preventing any gap between the base circle 12 b of the cam 12 and the roller 11.

Conversely, if the contact surfaces of the valve 4 and the valve seat 10 become worn, the biasing force of the valve spring 9 keeps acting on the adjusting screw 16 even while the base circle 12 b of the cam 12 faces the roller 11. Thus, the adjusting screw 16 protrudes by a smaller amount when the cam 12 further rotates after the cam lobe 12 a of the cam 12 presses down the arm 7 until the load is removed, than the amount by which the adjusting screw 16 is pushed in when the arm 7 is pressed down by the cam lobe 12 a of the cam 12. As a result, every time the cam 12 rotates once, the adjusting screw 16 is pushed in gradually, allowing the valve stem 5 to rise. This prevents any gap between the contact surfaces of the valve 4 and the valve seat 10.

With this lash adjuster 1, since the case 13 is rotationally fixed in position by the engagement between the anti-rotation protrusion 27 and the fitting port 26, when a load is applied to the adjusting screw 16 that tends to push in the adjusting screw, the case 13 never rotates. This prevents reduction in the valve lift due to rotation of the case 13. The lash adjuster thus stably performs its function. Also, the inner surface of the mounting hole 6 never becomes worn.

With this lash adjuster 1, when the lash adjuster 1 is inserted into the mounting hole 6, air between the bottom 17 of the case 13 and the inner bottom surface 24 of the mounting hole 6 is discharged through the air vent hole 25, so that the interior of the mounting hole 6 is kept at the atmospheric pressure, which prevents reaction force from acting on the bottom 17 of the case. Thus, the lash adjuster can be mounted easily in the cylinder head 2. Since one end of the air vent passage 25 is used as the fitting port 26, there is no need to form the fitting port 26 separately from the air vent hole 25, which makes easier to form the cylinder head 2.

With this lash adjuster 1, since engine oil flowing into the case through between the external thread 15 of the adjusting screw 16 and the internal thread 14 of the case 13 is discharged through the through hole 30 and then the air vent hole 25, soot and other contaminants mixed into engine oil is less likely to get stuck between the external thread 15 of the adjusting screw 16 and the internal thread 14 of the case 13, which makes the external thread 15 and the internal thread 14 less likely to become worn.

In this embodiment, the anti-rotation protrusion 27 provided on the bottom 17 of the case 13 is the anti-rotation protrusion 27 having the D-cut portion 28 on the outer periphery. But instead of this anti-rotation protrusion 27, as shown in FIGS. 4 and 5, an anti-rotation protrusion 32 having two chamfers 31 may be used. By engaging the two chamfers 31 with two chamfers 34 formed on the inner periphery of the fitting port 33, it is possible to prevent rotation of the case 13. With this arrangement, the anti-rotation protrusion 32 can be fitted in the fitting port 33 even when the case 13 is rotated by 180°, the lash adjuster 1 can be more easily mounted in the cylinder head 2. The two chamfers 31 are two flat surfaces that are parallel to a plane including the axis of the case 13.

Also, instead of the anti-rotation protrusion 27, as shown in FIGS. 6 and 7, an anti-rotation protrusion 35 in the shape of a regular polygonal column (such as a regular hexagonal column) 35 may be used. By engaging this anti-rotation protrusion 35 in a fitting port 36 in the shape of a regular polygonal column, it is possible to prevent rotation of the case 13. With this arrangement, the anti-rotation protrusion 35 can be fitted in the fitting port 36 at a plurality of different angular positions of the case 13, the lash adjuster 1 can be further easily mounted in the cylinder head 2.

As shown in FIGS. 8 and 9, the anti-rotation protrusion 27 may also be replaced by an anti-rotation protrusion 37 which is offset from the axis of case 13. This anti-rotation protrusion 37 is engaged in a fitting port 38 which is offset from the axis of the mounting hole 6 to prevent rotation of the case 13.

FIG. 10 shows a lash adjuster 41 according to the second embodiment of the present invention. As the anti-rotation protrusion 27 on the bottom 17 of the case 13, this lash adjuster 41 includes the same anti-rotation protrusion 27 as in the first embodiment, i.e. the one having the D-cut portion 28 on the outer periphery. Below, elements corresponding to those of the first embodiment are denoted by identical numerals and their description is omitted.

The adjusting screw 16 comprises a pivot member 16A axially slidably inserted in the case 13, an externally threaded member 16B supporting the end of the pivot member 16A inserted in the case 13 and having the external thread 15 on the outer periphery, and a disc spring 16C disposed between the pivot member 16A and the externally threaded member 16B.

The return spring 18 is a torsion coil spring having its bottom end engaged in an engaging hole 42 formed in the bottom 17 of the case 13, and its top end engaged in an engaging hole 43 formed in the externally threaded member 16B. Due to its torsional deformation, the return spring 18 applies torque to the externally threaded member 16B in the direction to push the pivot member 16A out of the case 13.

On the bottom 17 of the case 13, the anti-rotation protrusion 27 having the D-cut portion 28 on the outer periphery. The anti-rotation protrusion 27 is engaged in the fitting port 26 formed in the inner bottom surface 24 of the mounting hole 6.

With this lash adjuster 41, as with the first embodiment, since the rotation of the case 13 is prevented by the engagement of the anti-rotation protrusion 27 in the fitting port 26, it is possible to prevent reduction in the valve lift due to rotation of the case 13, so that the lash adjuster can stably perform its function.

With this lash adjuster 41, when the engine stops at a high temperature and the engine cools down later, thus producing differences in shrinkage between component parts of the valve lifter, the disc spring 16C between the externally threaded member 16B and the pivot member 16A is compressed, thus absorbing the differences in shrinkage. Thus, when the engine is restarted, no gap is produced between the valve 4 and the valve seat 10 due to the shrinkage differences between component parts of the valve lifter, which prevents pressure leakage.

If the return spring 18 is a torsion coil spring, the return spring 18 may be a cylindrically wound one as shown in FIG. 10, or a conically wound one as shown in FIG. 11.

As shown in FIGS. 12 to 14, the return spring 18 may be a torsion spring other than a torsion coil spring.

The return spring 18 shown in FIGS. 12 and 13 is a volute spring formed by helically winding a thin sheet material. This return spring 18 has its radially outer end rotationally fixed to the bottom 17 of the case 13, and its radially inner end fitted in a slit formed in a protrusion 44 at the end of the externally threaded member 16B inserted in the case 13. Due to its torsional deformation, the return spring 18 applies torque to the externally threaded member 16B in the direction to push the pivot member 16A out of the case 13. The external thread 15 on the outer periphery of the externally threaded member 16B and the internal thread 14 on the inner periphery of the case 13 are vertically symmetrical trapezoidal threads.

The return spring 18 shown in FIG. 14 is a spiral spring formed by spirally winding a thin sheet material. This return spring 18 has its radially outer end rotationally fixed to the bottom 17 of the case 13, and its radially inner end fitted in a slit formed in a protrusion 45 at the end of the externally threaded member 16B inserted in the case 13. Due to its torsional deformation, the return spring 18 applies torque to the externally threaded member 16B in the direction to push the pivot member 16A out of the case 13. The external thread 15 on the outer periphery of the externally threaded member 16B and the internal thread 14 on the inner periphery of the case 13 are vertically symmetrical triangular threads.

In the above embodiments, the bottom 17 of the case 13 may be integral with the case body as shown. But the bottom 17 of the case 13 may be formed separately from the case body and fixed to the bottom of case body.

FIGS. 15 and 16 show a lash adjuster 51 according to the third embodiment of the present invention.

In this embodiment, the outer bottom surface 52 of the case 13 is in contact with the inner bottom surface 24 of the mounting hole 6 so as to support an axial load applied to the case 13 on the inner bottom surface 24 of the mounting hole 6. A plurality of linear oil film expelling grooves 53 are formed on the outer bottom surface 52 of the case 13.

With this lash adjuster 51, although torque is produced between the pressure flanks 19 of the external thread 15 and the internal thread 14 when a load is applied to the adjusting screw 16 that tends to push in the adjusting screw, the frictional resistance between the outer bottom surface 52 of the case 13 and the inner bottom surface 24 of the mounting hole 6 prevents rotation of the case 13.

When a load is applied to the adjusting screw 16 from the arm 7 that tends to push in the adjusting screw, engine oil present between the outer bottom surface 52 of the case 13 and the inner bottom surface 24 of the mounting hole 6 is released into the oil film expelling grooves 53. This prevents formation of oil film between the outer bottom surface 52 of the case 13 and the inner bottom surface 24 of the mounting hole 6 due to the squeezing effect, which in turn ensures sufficient frictional resistance between the outer bottom surface 52 and the inner bottom surface 24.

In this embodiment, in order to ensure sufficient frictional resistance between the bottom 17 of the case 13 and the inner surface of the mounting hole 6, the oil film expelling grooves 53 are formed in the outer bottom surface 52 of the case 13. But instead, as shown in FIG. 17, the outer bottom surface 52 of the case 13 may be satin-finished. With this arrangement, compared to an arrangement in which the outer bottom surface 52 is flat and smooth, the outer bottom surface 52 has a higher friction coefficient, so that it is possible to ensure sufficient frictional resistance between the outer bottom surface 52 and the inner bottom surface 24.

When a load is applied to the adjusting screw 16 from the arm 7 that tends to push in the adjusting screw, engine oil present between the outer bottom surface 52 and the inner bottom surface 24 is released into recesses and protrusions of the satin-finished surface. This prevents formation of oil film between the outer bottom surface 52 and the inner bottom surface 24 due to the squeezing effect, which in turn ensures sufficient frictional resistance between the outer bottom surface 52 and the inner bottom surface 24.

The outer bottom surface 52 of the case 13 may be satin-finished by electric discharge machining or laser machining. But preferably, it is satin-finished by shot peening, because shot peening hardens the outer bottom surface 52 of the case 13, thereby increasing its wear resistance, which in turn makes it possible to maintain frictional resistance between the outer bottom surface 52 and the inner bottom surface 24 over an extended period of time.

As shown in FIG. 18, the bottom 17 of the case 13 may have a tapered outer peripheral surface 55 having a downwardly decreasing diameter and engaged in a tapered inner peripheral surface 54 formed on the mounting hole 6 and having a downwardly decreasing diameter so as to support an axial load applied to the case 13 on the tapered inner peripheral surface 54.

With this arrangement, when a load is applied to the adjusting screw 16 from the arm 7 that tends to push in the adjusting screw, high surface pressure is produced between the tapered outer peripheral surface 55 and the tapered inner peripheral surface 54 due to the wedge effect, which ensures sufficient frictional resistance between the tapered outer peripheral surface 55 and the tapered inner peripheral surface 54.

As shown in FIG. 19, a recess 56 may be formed in the outer bottom surface 52 of the case 13 except its peripheral edge so that only the peripheral edge of the outer bottom surface 52 of the case 13 contacts the inner bottom surface 24 of the mounting hole 6.

With this arrangement, when a load is applied to the adjusting screw 16 from the arm 7 that tends to push in the adjusting screw 16, frictional resistance produced between the outer bottom surface 52 of the case 13 and the inner bottom surface 24 of the mounting hole 6 concentrates on the radially outer side, so that it is possible to ensure sufficient frictional resistance for preventing rotation of the case 13.

Similarly, a recess (not shown) may be formed in the inner bottom surface 24 of the mounting hole 6 except its peripheral edge so that only the peripheral edge of the inner bottom surface 24 of the mounting hole 6 contacts the outer inner bottom surface 52 of the case 13. With this arrangement too, frictional resistance produced between the outer bottom surface 52 of the case and the inner bottom surface 24 of the mounting hole 6 concentrates on the radially outer side, so that it is possible to ensure sufficient frictional resistance for preventing rotation of the case 13.

As shown in FIG. 20, the bottom 17 of the case 13 may be press-fitted (i.e. fitted with an interference) into a small-diameter inner peripheral portion 57 formed on the mounting hole 6 and having a smaller diameter than the outer diameter of the bottom 17 of the case 13.

With this arrangement, high surface pressure is produced between the bottom 17 and the small-diameter inner peripheral portion 57 due to press fitting, which ensures sufficient frictional resistance between the bottom 17 of the case 13 and the inner surface of the mounting hole 6.

Since the case 13 is fitted without interference at its portion above the bottom 17, it is possible to minimize the possibility of deformation of the internal thread 14 when the case is press-fitted. In order to minimize deformation of the internal thread 14 when the case is press-fitted, a large-diameter outer peripheral portion (not shown) may be formed on the bottom 17 of the case 13 which is press-fitted in the mounting hole 6. But with this arrangement, since the entire step of inserting the case 13 into the mounting hole 6 comprises press fitting, it is difficult to insert the case into the mounting hole. On the other hand, by inserting the bottom 17 of the case 13 into the small-diameter inner peripheral portion 57, only the last stage of the step of inserting the case 17 into the mounting hole 6 is press fitting, so that the case can be more easily inserted into the mounting hole.

As shown in FIG. 21, a sheet 58 made of rubber or an elastomer may be disposed between the outer bottom surface 52 of the case 13 and the inner bottom surface 24 of the mounting hole 6 so as to support an axial load applied to the case 13 on the sheet 58.

With this arrangement, the frictional resistance between the outer bottom surface 52 and the inner bottom surface 24 is higher than when the outer bottom surface 52 is in direct contact with the inner bottom surface 24, so that it is possible to ensure sufficient frictional resistance for preventing rotation of the case 13.

As shown in FIG. 22, a seat 59 made of iron may be mounted in the mounting hole 6 so that the seat 59 forms the inner bottom surface 24 of the mounting hole 6, and supports an axial load applied to the case 13 thereon.

With this arrangement, since the inner bottom surface 24 of the mounting hole 6 is made of iron, even if the cylinder head is made of aluminum, the inner bottom surface 24 of the mounting hole 6 is less likely to become worn. This minimizes reduction with time in friction coefficient of the inner bottom surface 24, and thus ensures sufficient frictional resistance between the bottom 17 of the case 13 and the inner surface of the mounting hole 6.

As shown in FIG. 23, a cylindrical iron sleeve 61 having a bottom and formed with the amounting hole 6 may be press-fitted in a base hole 60 formed in the top surface of the cylinder head 2 so as to support an axial load applied to the case 13 on the sleeve 61.

With this arrangement, since the inner surface of the mounting hole 6 is made of iron, even if the cylinder head 2 is made of aluminum, the inner surface of the mounting hole 6 is less likely to become worn. This ensures sufficient frictional resistance between the bottom 17 of the case 13 and the inner surface of the mounting hole 6. Also, there is no difference in shrinkage between the sleeve 61 and the case 13, even when the ambient temperature rises, the case 13 remains strongly engaged in the mounting hole 6. 

1. A lash adjuster comprising a cylindrical case (13) having a bottom (17) and received in a mounting hole (6) formed in a top surface of a cylinder head (2), said case (13) having an internal thread (14) on an inner periphery thereof, an adjusting screw (16) having an external thread (15) on an outer periphery thereof which is in threaded engagement with the internal thread (14) of the case (13), and a return spring (18) disposed between the adjusting screw (16) and the bottom (17) of the case (13) and biasing the adjusting screw (16) in a direction to protrude upwardly from the case (13), said adjusting screw (16) having a protruding end (22) protruding from the case (13) and configured to pivotally support an arm (7) of a valve gear, characterized in that the lash adjuster further comprises an anti-rotation part arranged to prevent rotation of the case (13).
 2. The lash adjuster of claim 1 wherein said anti-rotation part comprises an anti-rotation protrusion (27) provided on the bottom (17) of the case (13), and a fitting port (26) formed in an inner bottom surface (24) of the mounting hole (6), said anti-rotation protrusion (27) being fitted in the fitting port (26).
 3. The lash adjuster of claim 2 wherein said anti-rotation protrusion is a protrusion (27) having a D-cut portion (28) on an outer periphery thereof.
 4. The lash adjuster of claim 2 wherein said anti-rotation protrusion is a protrusion (32) having two chamfers (31) on an outer periphery thereof.
 5. The lash adjuster of claim 2 wherein said anti-rotation protrusion is a protrusion (35) in the shape of a regular polygonal column.
 6. The lash adjuster of claim 2 wherein said anti-rotation protrusion is a protrusion (37) offset from an axis of the case (13).
 7. The lash adjuster of claim 2 wherein said fitting port (26) is one end of an air vent hole (25) extending from the inner bottom surface (24) of the mounting hole (6) to outside.
 8. The lash adjuster of claim 7 wherein a through hole (30) extends vertically through the bottom (17) of the case(13), with a bottom end thereof open to a free end of the anti-rotation protrusion (27).
 9. The lash adjuster of claim 1 wherein said anti-rotation part is a friction ensuring part configured to ensure frictional resistance between the bottom (17) of the case (13) and the inner surface of the mounting hole (6), thereby preventing rotation of the case (13).
 10. The lash adjuster of claim 9 wherein said friction ensuring part comprises an oil film expelling groove (53) formed in an outer bottom surface (52) of the case (13).
 11. The lash adjuster of claim 9 wherein said friction ensuring part comprises a satin-finished surface formed on an outer bottom surface (52) of the case (13).
 12. The lash adjuster of claim 11 wherein said satin-finished surface is formed by shot peening.
 13. The lash adjuster of claim 9 wherein said friction ensuring part comprises a tapered outer peripheral surface (55) formed on the bottom (17) of the case (13) and having a downwardly decreasing diameter, and a tapered inner peripheral surface (54) formed on the mounting hole (6) and having a downwardly decreasing diameter, said tapered outer peripheral surface (55) being engaged in the tapered inner peripheral surface (54).
 14. The lash adjuster of claim 9 wherein said friction ensuring part comprises a recess (56) formed in an outer bottom surface (52) of the case (13) except its peripheral edge, or a recess formed in an inner bottom surface (24) of the mounting hole (6) except its peripheral edge.
 15. The lash adjuster of claim 9 wherein said friction ensuring part comprises a small-diameter inner peripheral portion (57) formed on the mounting hole (6), said bottom (17) of the case (13) being press-fitted in the small-diameter inner peripheral portion (57).
 16. The lash adjuster of claim 9 wherein said friction ensuring part comprises a sheet (58) made of rubber or an elastomer and disposed between an outer bottom surface (52) of the case (13) and an inner bottom surface (24) of the mounting hole (6).
 17. The lash adjuster of claim 9 wherein said friction ensuring part comprises a seat (59) made of iron and forming an inner bottom surface (24) of the mounting hole (6).
 18. The lash adjuster of claim 9 wherein said friction ensuring part comprises a sleeve (61) made of iron and forming the mounting hole (6).
 19. The lash adjuster of claim 1 wherein said return spring (18) is a compression coil spring that applies an axial force to the adjusting screw (16) that tends to push the adjusting screw (16) out of the case (13).
 20. The lash adjuster of claim 1 wherein said return spring (18) is a torsion spring that applies torque to the adjusting screw (16) that tends to push the adjusting screw (16) out of the case (13).
 21. The lash adjuster of claim 20 wherein said torsion spring is one of a torsion coil spring, a spiral spring and a volute spring.
 22. The lash adjuster of claim 1 wherein said external thread (15) and the internal thread (14) are triangular threads, trapezoidal threads or serration-shaped threads. 